The objective of the proposed research is the detailed examination of specific cytoplasmic protein synthesis which occurs in the G1-phase of the cell cycle and is required for progression of cells into S phase. The temporal synthesis of these protein in (A) synchronous control cells, (B) cells released from arrest by physiologic means (e.g., nutrient- or serum-deprivation), (C) cells recovering from delay induced by hyperthermia treatment, and (D) Cells released from block by the anti-metabolites cycloheximide or lucanthone will be examined by high resolution two-dimensional polyacrylamide gel electrophoresis (PAGE). Proteins synthesized at particular times in G1 will be isolated in quantities sufficient for physical-chemical characterization, and for bioassay, i.e., the ability to induce DNA synthesis in quiescent cells. Studies on hyperthermia-delayed cells will focus on determination of critical protein (probably enzyme) targets for hyperthermia damage as well as investigation of the hypothesis that thermotolerance is conferred by the specific synthesis or accumulation of stabilizing proteins.